I think the size vs. rubbing issue has been addressed, sooo....

If you know the width of your tire, most tire manufactures will give a range of rim widths that their particular size of tire will fit (in other words, a Bridgestone 275W tire might fit an 8" rim, but a Nitto 275W might not). They also give a recommended rim width somewhere within that range that would best fit the tire.

Check with the manufacturers before you buy, most of them will list it on their sites, or tirerack.com usually has that info listed as well.